The present invention relates to a method for producing a marking on a pipe and also to a pipe bending machine for producing such a marking.
More particularly, it relates to a method and a pipe bending machine which has a feeding carriage unit reciprocable in longitudinal direction of a pipe and also movable in a transverse direction, and having a rotatable clamping device for clamping the pipe, a turnable bending table provided with a bending mold with clamping jaws, and a sliding rail associated with the bending mold. During bending of a pipe, the initial pipe is longer than the pipe which has been bent and is to be used, since a pipe to be bent must be clamped at its front end by clamping jaws on the bending mold and at its rear end by a clamping sleeve of the feeding carriage unit. Therefore, in many cases the bent pipe must be cut off at is front end and frequently at its rear end. Since the location of the clamping is not visible on the pipe in many cases, there is a difficulty in finding the points on the pipe in which the pipe must be cut off. For determining this, the pipe after bending is inserted into the form, in which the points of the cuts to be made can be identified. The operator draws at the respective locations of the pipe in correspondence with the form respective marks wherein the pipe is to be cut off.
A bent pipe is however not only to be cut at both ends or at one end. Mounting flanges for other holders must be mounted on the bent pipe as well. These objects are to be arranged not only on one end or both ends of the pipe, but in most cases they are distributed over the length of the pipe. For example, these objects are holders which must be attached to the pipe mainly by welding so as to connect the pipe by screwing to a support on the chassis in the event of an exhaust pipe of a power vehicle. The points at which the holders or similar mounting elements must be attached are determined conventionally by inserting the finished pipe into a form and providing markings manually in accordance with the form for attaching the holders or similar objects to the pipe. This operation is expensive and inaccurate. First of all, the manufacture of such a form is expensive. Since pipes are bent in a program on a pipe bending machine in many spatial shapes, therefore the forms must be provided with the respective plurality of shapes. This not only brings high cost for manufacturing of the forms but also the finished forms occupy a great space, and their storage and handling is complicated. Therefore, in many cases a sufficient accuracy for placing holders or other objects onto forms is compromised, and marking is produced on the pipe by a measuring device which in a simple case can be a foot rule. The use of a measuring device which must be adjusted for each spatial shape of the pipe, or the use of a foot rule is a source of errors in the manufacture, especially in mass production since it involves frequently a monotonous work which reduces concentration and thereby leads to faulty measurements and faulty judgments. Such a monotonous work requires a longer time for determination of the error and therefore the errors are connected with considerable losses in practice.